A shaft of an electrical motor is mounted on bearings at both of its ends. The bearings are typically supported by the end shields of the motor housing. When a bearing breaks down, the electrical motor can be damaged and eventually totally immobilized. In e.g. railway traction motor applications this means a stand still of the train and expensive measures to get a repair of the motor done either in situ or in a repair shop, in which case the locomotive must be transported by a service train or lifted off the track. These measures are clearly both expensive and time consuming.
In an electrical motor where grease from the bearing is prevented from entering the interior of the motor housing a conventional solution is either a rubber lip seal or a labyrinth seal. A lip seal is a wearing part and a labyrinth seal is a complicated component with high friction losses.